Assays for detecting the presence and level of a variety of analytes in body fluid samples are known. Such assays are often designed for simplicity of use so that they can be reliably conducted in a doctors office or other clinical setting where personnel may have little training in clinical assay procedure or in interpreting assay results. In order to minimize the need for operator involvement, it is preferable that the assay be carried out in an automated or self-contained manner.
Such self-contained assays have typically been limited, for the sake of simplicity of operation, to one-step assay procedures. A number of useful assays, however, are multistage in nature, requiring more than one reacting or binding step. Further, one or more of the steps may be rate limiting, or affected by localized reagent concentrations. Typically, multistage assays are less readily automated and generally require more input from the user, thus increasing the possibility of error.
It is therefore desirable to provide an automated, self-contained assay device which is able to perform multistage assays, in particular those containing multiple reacting or binding steps in which one or more of the steps is rate limiting or the final assay result is affected by localized reagent of analyte concentrations.